using System;

using System.Collections.Concurrent;

using System.Threading.Tasks;

using System.Threading;

​

class Program

{

    private static ConcurrentDictionary<string, Lazy<Task>> tokenValidations =

    new ConcurrentDictionary<string, Lazy<Task>>();

​

    public static int index = 0;

​

    static async Task Main(string[] args)

    {

        var tasks = new[]

        {

            ValidateTokenAsync("AAAAA"),

            ValidateTokenAsync("AAAAA"),

            ValidateTokenAsync("BBBBB"),

            ValidateTokenAsync("CCCCC"),

            ValidateTokenAsync("AAAAA"),

            ValidateTokenAsync("AAAAA"),

            ValidateTokenAsync("EEEEE"),

            ValidateTokenAsync("AAAAA"),

            ValidateTokenAsync("GGGGG"),

            ValidateTokenAsync("HHHHH"),

            ValidateTokenAsync("ZZZZZ"),

            ValidateTokenAsync("AAAAA"),

            ValidateTokenAsync("AAAAA")

        };

​

        await Task.WhenAll(tasks);

​

        Console.Write($"\nFin with index: {index}");

    }

​

    public static async Task ValidateTokenAsync(string token)

    {

        var validationTask = tokenValidations.GetOrAdd(token, _ => new Lazy<Task>(() => RefreshToken(token), LazyThreadSafetyMode.ExecutionAndPublication));

        await validationTask.Value;

    }

​

    private static async Task RefreshToken(string token)

    {

        Console.WriteLine($"Thread {Thread.CurrentThread.ManagedThreadId} is refreshing token: {token} \n");

        index++;

    }

}

​